1. Field of the Invention
The present invention is related to real-time vital sign monitoring devices. More specifically, the present invention relates to a device for monitoring a user's vital signs and using an accelerometer to filter the vital sign signal.
2. Description of the Related Art
There is a need to know how one is doing from a health perspective. In some individuals, there is a daily, even hourly, need to know one's health. The prior art has provided some devices to meet this need.
One such device is a pulse oximetry device. Pulse oximetry is used to determine the oxygen saturation of arterial blood. Pulse oximeter devices typically contain two light emitting diodes: one in the red band of light (660 nanometers) and one in the infrared band of light (940 nanometers). Oxyhemoglobin absorbs infrared light while deoxyhemoglobin absorbs visible red light. Pulse oximeter devices also contain sensors that detect the ratio of red/infrared absorption several hundred times per second. A preferred algorithm for calculating the absorption is derived from the Beer-Lambert Law, which determines the transmitted light from the incident light multiplied by the exponential of the negative of the product of the distance through the medium, the concentration of the solute and the extinction coefficient of the solute.
The major advantages of pulse oximetry devices include the fact that the devices are non-invasive, easy to use, allows for continuous monitoring, permits early detection of desaturation and is relatively inexpensive. The disadvantages of pulse oximetry devices are that it is prone to artifact, it is inaccurate at saturation levels below 70%, and there is a minimal risk of burns in poor perfusion states. Several factors can cause inaccurate readings using pulse oximetry including ambient light, deep skin pigment, excessive motion, fingernail polish, low flow caused by cardiac bypass, hypotension, vasoconstriction, and the like.
In monitoring one's health there is a constant need to know how many calories have been expended whether exercising or going about one's daily routine. A calorie is a measure of heat, generated when energy is produced in our bodies. The amount of calories burned during exercise is a measure of the total amount of energy used during a workout. This can be important, since increased energy usage through exercise helps reduce body fat. There are several means to measure this expenditure of energy. To calculate the calories burned during exercise one multiplies the intensity level of the exercise by one's body weight (in kilograms). This provides the amount of calories burned in an hour. A unit of measurement called a MET is used to rate the intensity of an exercise. One MET is equal to the amount of energy expended at rest.
For example, the intensity of walking 3 miles per hour (“mph”) is about 3.3 METS. At this speed, a person who weighs 132 pounds (60 kilograms) will burn about 200 calories per hour (60×3.3=198).
The computer controls in higher-quality exercise equipment can provide a calculation of how many calories are burned by an individual using the equipment. Based on the workload, the computer controls of the equipment calculate exercise intensity and calories burned according to established formulae.
The readings provided by equipment are only accurate if one is able to input one's body weight. If the machine does not allow this, then the “calories per hour” or “calories used” displays are only approximations. The machines have built-in standard weights (usually 174 pounds) that are used when there is no specific user weight.
Current outpatient continuous, mobile, ambulatory diagnostic monitoring for Heart Rate disease and abnormal conditions such as Bradycardia (slow heart rate), Tachycardia (high heart rate) heart arrhythmia and sleep apnea among others, use an Electrocardiogram (ECG) type device such as a Holter Monitor or a finger mounted pulse dosimeter specially configured for data collection. These devices are normally worn for an extended period by the patient, often as much as 24-48 hours. Holter Monitors consist of a body harness, multiple stick-on electrodes and a large battery and data collection module. The device monitors and collects heart rate data as well as collecting the ECG waveform signal for post analysis and diagnosis by a cardiologist. The finger mounted pulse oximeter has a chest strap that holds a large battery and data collection module. Both devices are cumbersome and restrictive of movement and performance of simple daily tasks. The pulse oximeter is susceptible to motion artifacts eradicating the heart rate signal.